This invention relates to the conversion of high-boiling hydrocarbons in the presence of a hydrocarbon solvent at mixture supercritical conditions using hot particle heating.
The conversion of high boiling hydrocarbons is economically important in maximizing the production of useable hydrocarbons. Useable hydrocarbons for these purposes are defined as hydrocarbons possessing normal boiling points less than 538° C. (1000° F.). Methods traditionally employed to enhance the recovery of useable hydrocarbons include thermal cracking, visbreaking, hydrocracking, catalytic cracking, steam cracking, and solvent extraction to name a few.
Cracking is a refining process involving the decomposition and molecular recombination of hydrocarbons, to form molecules suitable for motor fuels, monomers, and other petrochemicals. Generally, there are two types of cracking operations: (1) thermal cracking, whereby hydrocarbon feedstocks are exposed to high temperatures, on the order of 538° to 649° C. (1000° to 1200° F.), for varying periods of time, and (2) catalytic cracking, whereby hydrocarbon vapors at a temperature of approximately 399° C. (750° F.) are passed over a catalyst. Another process for the improvement of high boiling hydrocarbons is visbreaking, which consists of the thermal cracking of heavy oils, which are pyrolyzed, or cracked, under relatively mild conditions to produce products having lower viscosities. Typical process conditions include heating the heavy oil to between 427° and 524° C. (800° and 975° F.), at pressures between about 4.5 and 7.9 megapascals, absolute (MPaa) (65 and 1000 psia). As used herein, pressures given are absolute (or differential) unless gauge (g) is indicated.
There are several examples in the prior art demonstrating methods for the treatment and upgrading of high boiling hydrocarbons at or near critical conditions. There are several examples of the use of thermal cracking of high boiling hydrocarbons at or near critical conditions of the solvent. In U.S. Pat. No. 3,310,484, Mason et al. disclose the conversion of crude residua, asphaltenes, aromatic tars, and the like to lower boiling hydrocarbons. In U.S. Pat. No. 4,483,761, Paspek, Jr. discloses a process by which heavy hydrocarbons are cracked at temperatures greater than or equal to the critical temperature of the solvent. In U.S. Pat. No. 4,592,826, Ganguli discloses a non-catalytic process for upgrading materials such as coal, residual oils, tars sands and shale oils. In U.S. Pat. No. 4,615,791, Choi et al. disclose a method for visbreaking heavy oils using hydrogen donor hydrocarbon solvents at or near supercritical conditions. In U.S. Pat. No. 4,944,863, Smith et al. disclose a method for treating resids or heavy stocks by thermally hydrocracking the materials under conditions where the solvent is substantially in its supercritical or dense supercritical state. In U.S. Pat. No. 5,370,787, Forbus et al. disclose a method for thermal treatment of petroleum residua at elevated temperatures and pressures. In U.S. Pat. No. 5,443,715, Grenoble et al. disclose a method for upgrading steam cracker tars, using hydrogen donor diluents to prevent the thermal degradation reactions. In U.S. Pat. No. 5,496,464, Piskorz et al. disclose a method for conversion of heavy hydrocarbon oils in supercritical fluids, specifically catalytic conversion at temperatures and pressures at or greater than the critical temperature and pressure of the solvent. In U.S. Pat. No. 5,725,756, Subramanian et al. disclose the reduction of coke buildup in catalysts at near critical and supercritical conditions for the solvent.
Similarly, the prior art also shows examples of the extraction of high-boiling hydrocarbons under supercritical conditions. See for example, U.S. Pat. No. 4,341,619 to Poska, disclosing the supercritical extraction of tar sands at supercritical conditions in a mobile bed; U.S. Pat. No. 4,354,922 to Derbyshire et al., disclosing the integrated extraction of petroleum residua, refractory bottoms and coal to gasoline and middle distillate products under supercritical conditions; U.S. Pat. No. 4,376,693 to Warzel, disclosing the extraction of solid particulate material such as oil shale; and U.S. Pat. No. 4,482,453 to Coombs and U.S. Pat. No. 4,890,411 to Buccilli disclosing supercritical solvent extractions of deposits.
In addition, there are examples disclosing the hydrotreatment of high boiling hydrocarbons under supercritical conditions. The resulting product streams are rich in hydrocarbon product streams having lower boiling points relative to the feed streams. In U.S. Pat. Nos. 6,123,835 and 6,428,686, Ackerson et al. disclose a method by which the addition of hydrogen gas over a catalyst in a hydrotreatment processes is eliminated through the mixing of the oil to be treated with a solvent or diluent having the ability to “donate” hydrogen from the molecular structure of the solvent to the molecular structure of the heavy hydrocarbons, thereby providing a hydrogen source for the hydrotreatment process.
In each of the examples presented, the cracking/extraction/hydrotreatment of the high boiling hydrocarbon feed occurs generally at or near the supercritical conditions of the solvent. The present invention, however, converts high boiling hydrocarbons at or above the supercritical temperature and pressure of the feedstock-solvent mixture.
In the prior art, the low molecular weight constituents of petroleum or other hydrocarbon sources are typically recovered as shown in FIG. 1 by atmospheric distillation 10 to obtain straight run naphtha, distillates, gas oil, atmospheric resid, and the like. The atmospheric tower bottoms (ATB) residue 12 is usually further processed to increase the overall yield of the more valuable products, e.g. naphtha, distillates and gas oil. The ATB residue can contain a large portion of hydrocarbons boiling above 538° C. (1000° F.), as well as nitrogen, sulfur, organometallic compounds, and Conradson Carbon Residue (CCR), making it difficult to process. Frequently, a vacuum distillation tower 14 is employed to recover vacuum gas oil (VGO) 28. The vacuum tower bottoms (VTB) residue 16 is even more concentrated in high-boiling hydrocarbons, e.g. 538° C.+ (1000° F.+) hydrocarbons, as well as Conradson Carbon Residue (CCR), sulfur, nitrogen and organometallic compounds.
In typical refinery processing with a vacuum distillation tower 14, the VTB residue 16 (and/or the ATB) is fed to solvent deasphalting 18, a coker 20 and/or a hydrocracker 22 in various proportions, orders or combinations. The solvent deasphalting 18 contacts the residue with propane, butane, pentane or a like hydrocarbon solvent (either subcritical or supercritical, e.g. residuum oil supercritical extraction (ROSE) or conventional solvent deasphalting (DEMEX or SOLVAHL)) to separate deasphalted oil (DAO) 24 (and/or resins) from the asphaltenes 26. The DAO 24 has a lower CCR, sulfur, nitrogen and metals content than the atmospheric resid/vacuum resid feed.
The coker 20 subjects the VTB residue 16, the asphaltenes 26 from the solvent deasphalting 18, or a combination thereof, to thermal cracking and soaking at high temperature, e.g. 482° to 510° C. (900° to 950° F.), usually near atmospheric pressure, generally without solvent present. The vapors recovered and condensed are generally lower molecular weight products. A solid residue, known as coke, is formed in substantial quantities. Generally, coke only has solid fuel value.
The resid hydrocracker 22 receives the hydrocarbon feed and typically operates at about 6.9 to 20.7 MPaa (1000 to 3000 psia) and about 343° to 427° C. (650° to 800° F.), in the presence of a hydrocracking catalyst, with molecular hydrogen added from a hydrogen generation unit 27, to form lower molecular weight products while at the same time removing substantial amounts of CCR and sulfur, primarily in the form of H2S, as well as nitrogen and organometallic compounds. A hydrogen consumption of 178 to 356 standard cubic meters per cubic meter of oil (1000 to 2000 standard cubic feet per (42-gallon) barrel (SCFB) of oil) is typical. High pressure is needed to ensure the presence of hydrogen in the reaction mixture and the formation of insignificant amounts of coke, and high levels of feed CCR and/or metals present in the hydrocracker feed can easily poison the catalyst. Because of the potential for catalyst poisoning, a cheap but less effective catalyst is usually used in the hydrocracker 22, resulting in incomplete conversion of the high molecular weight compounds.
The low molecular weight products 28 from the vacuum tower 14, the coker 20 and the hydrocracker 22, as well as DAO 24 from the solvent deasphalting 18, are usually further processed in hydrotreaters or gas oil hydrocrackers 30 requiring large amounts of molecular hydrogen to catalytically upgrade the hydrocarbons and remove additional nitrogen and sulfur. Because the feed to the hydrocracker 30 has been pretreated to remove catalyst poisons, a more effective and more expensive catalyst can be used. A typical operating condition is approximately 10.3 MPaa (1500 psia) and 371° to 454° C. (700° to 850° F.).
Gas oil 32 from the atmospheric tower 10 and the hydrocracker 30 is then usually cracked in a fluidized catalytic cracking (FCC) unit 34, well known in the art, to produce additional naphtha and distillate.